The present invention relates to an improved interlayer product for the preparation of laminated safety glass. More particularly, the invention relates to an interlayer product for laminated safety glass whereby multiple layers of film having the desired properties of thickness, dimensional stability and surface pattern are combined, by applying water drops as an array in the transverse and machine directions.
In laminated safety glass used in window glass for buildings and such, it is not uncommon for the laminator to use thicker interlayer than typically used in automotive applications, which is nominally 0.76 mm (30 mils) thick. Further, it is not unusual to combine multiple layers of interlayer to achieve a thicker product for enhanced structural and acoustic properties.
The extrusion process for the production of thick interlayer, that is, greater than 0.76 mm (30 mils), requires high throughput rates and low line speeds that are not cost effective. The process results in product with deficiencies in dimensional stability, such as shrinkage, difficulty in winding and cutting, additional manufacturing transitions and problems in generating the surface pattern necessary for proper de-airing when laminating the glass/interlayer construction.
Typically multi-ply product as described in our Application PCT/US98/26425, filed Dec. 11, 1998, which is incorporated by reference herein, (referred to hereinafter as Application FA-0782), while overcoming the problems of extrusion noted above, does not always process well with automated unwinding equipment because the lightly bonded plies can be separated due to nip roil misalignments and unmatched speeds within the equipment.
Further, other types of surface patterns, such as, embossed and serrated, do not work well with the multi-plying process as described in Application FA-0782.
It has now been found if drops of water are deposited in an array in the transverse and machine directions when combining the interlayer plies by a process as described in FA-0782, the resulting structure is more robust and may be handled as an integral unit in any type of lamination equipment without separating.
Further, by appropriately selecting the array and size of the water drops, a broad range of bonding strengths between the sheets can be achieved while still providing adequately un-bonded or lightly bonded areas for de-airing in the lamination process.
Further, because water is not an intrusive material to polyvinyl butyral resin (PVB), the water drops are completely absorbed and diffused and do not create subsequent processing problems.
Further, the technique can be applied to many surface pattern type of PVB sheeting, although bonding is affected by the degree of roughness.
In the process of the present invention, two or more rolls of sheeting comprising polyvinyl butyral as the primary component with plasticizers as the secondary component are simultaneously unwound and rewound together. The process is operated under controlled tension, line speed and temperature so that the edges of the respective layers are aligned and roll formation is normal, the tension on the respective sheets is equal, thickness is maintained and entrapped air is minimized.
Further, prior to the combining of the sheeting at windup, water is applied as an array of drops through a dosing apparatus in the transverse and machine directions of the sheeting. The application of the water is made by pulsing the dosing units so as to apply the drops periodically in the machine direction. The resulting product is used to produce laminated safety glass with thick interlayer construction.
More particularly, by varying the number of dosing units in the cross-web direction and the pulsing frequency to control the machine direction application, a composite structure with variable controlled bonding between the layers can be produced.